The commonly-owned International Patent applications no. WO 01/23104 and WO 02/078388, the disclosure of which is hereby incorporated by reference, describe an array of transducers and their use to achieve a variety of effects. They describe methods and apparatus for taking an input signal, replicating it a number of times and modifying each of the replicas before routing them to respective output transducers such that a desired sound field is created. This sound field may comprise, inter alia, a directed, steerable beam, focussed beam or a simulated origin. The methods and apparatus of the above and other related applications is referred to in the following as “Sound Projector” technology.
Conventional surround-sound is generated by placing loudspeakers at appropriate positions surrounding the listener's position (also known as the “sweet-spot”). Typically, a surround-sound system employs a left, centre and right speaker located in the front halfspace and two rear speakers in the rear halfspace. The terms “front”, “left”, “centre”, “right” and “rear” are used relative to the listener's position and orientation. A subwoofer is also often provided, and it is usually specified that the subwoofer can be placed anywhere in the listening environment.
A surround-sound system decodes the input audio information and uses the decoded information to distribute the signal among different channels with each channel usually being emitted through one loudspeaker or a combination of two speakers. The audio information can itself comprise the information for each of the several channels (as in Dolby Surround 5.1) or for only some of the channels, with other channels being simulated (as in Dolby Pro Logic Systems).
In the commonly-owned published international patent applications no. WO 01/23104 and WO 02/078388 the Sound Projector generates the surround-sound environment by emitting beams of sound each representing one of the above channels and reflecting such beams from surfaces such as ceiling and walls back to the listener. The listener perceives the sound beam as if emitted from an acoustic mirror image of a source located at or behind the spot where the last refection took place. This has the advantage that a surround sound system can be created using only a single unit in the room.
Whereas Sound Projector systems that use the reflections of acoustic beams can be installed by trained installers and closely guided users, there remains a desire to facilitate the set-up procedure for less-trained personnel or the average end user.
The problems associated with the setting up of a Sound Projector are not related to certain known methods aiming at partial or total wavefield reconstruction. In the latter methods, it is attempted to record a full wavefield at the listener's position. For reproduction a number of loudspeakers are controlled in a manner that closest approximates the desired wavefield at the desired position. Even though these methods are inherently recording reflections from the various reflectors in a room or concert hall, no attempt is made to infer from these recordings control parameters for a Sound Projector. In essence, the wavefield reconstruction methods are “ignorant” as to the actual room geometry and therefore not applicable to the control problem underlying the present invention.
An important aspect of setting-up a Sound Projector, is determining suitable, or optimum, beam-steering angles for each output-sound-channel (sound-beam), so that after zero, one, or more bounces (reflections off walls, ceilings or objects) the sound beams reach the listener predominantly from the desired directions (typically from in-front, for the centre channel, from either side at the front for the left- and right-front channels, and from either side behind the listener, for the rear-left and right channels). A second important set-up aspect, is arranging for the relative delays in each of the emitted sound beams to be such that they all arrive at the listener time-synchronously, the delays therefore being chosen so as to compensate for the various path lengths between the Sound Projector array and the listener, via their different paths.
Important to performing this set-up task other than by trial and error, is detailed information about the geometry of the listening environment surrounding the Sound Projector and listener, typically a listening room, and in a domestic setting, typically a sitting room. Additional important information are the locations of the listener, and of the Sound Projector, in the environment, and the nature of the reflective surfaces in the surrounding environment, e.g. wall materials, ceiling materials and coverings. Finally, the locations of sound reflective and/or sound obstructive obstacles within the environment need to be known so as to be able to avoid sound-beam paths that intersect such obstacles accidentally.